CHICAGO - Mitch Trubisky threw for 166 yards and led three scoring drives after Mike Glennon struggled for Chicago, before the Denver Broncos scored two long touchdowns in the closing minutes to beat the Bears 24-17 in the preseason opener on Thursday night.

Though the Bears have insisted Glennon is their starter, Trubisky just might have created a quarterback controversy.

Denver’s Trevor Siemian did nothing to hurt his standing as the leader for the starting quarterback job, while Paxton Lynch did little to close any ground.

Third-stringer Kyle Sloter threw a 47-yard touchdown pass to Isaiah McKenzie with about six minutes left in the game, and De’Angelo Henderson ran for a 41-yard score with just under two minutes remaining to put the Broncos on top 24-17.

But the biggest development in this game was Trubisky showing exactly why general manager Ryan Pace traded up a spot with San Francisco to draft him with the No. 2 overall pick.

The North Carolina product completed 18 of 25 passes in his first pro appearance after making just 13 college starts.

Trubisky replaced veteran Mark Sanchez late in the second quarter and completed his first 10 passes while leading Chicago to touchdowns on his first two possessions and a field goal on the next one. That gave the Bears a 17-10 lead.

Glennon had a rough time in his first appearance for Chicago. Signed to a three-year contract after the Bears parted with Jay Cutler, he was 2 of 8 for 20 yards with a zero QB rating. Chris Harris Jr. intercepted an overthrown pass on the game’s third play from scrimmage and returned it 50 yards for a touchdown.

Things didn’t get much better for Chicago’s offense until Trubisky came in with 1:55 left in the half.

He completed four passes on a 50-yard drive, connecting with Victor Cruz from the 2 to cut it to 10-7 with 13 seconds left.

Trubisky then led Chicago on a 75-yard drive early in the third, going 5 for 5 for 50 yards before Benny Cunningham ran it in from the 1 to give Chicago a 14-10 lead.

Siemian — a surprise successor to Peyton Manning last season — completed 6 of 7 passes for 51 yards and led a field-goal drive.

Lynch came on early in the second quarter and was 6 for 9 for 42 yards.

INJURY UPDATE

Broncos: The Broncos held out five-time Pro Bowl linebacker Von Miller and were missing S T.J. Ward (hamstring), LB Todd Davis (shoulder), C Matt Paradis (hip) and RB Jamaal Charles (knee). … DE Billy Winn left the field on a cart late in the first quarter with a right knee injury. He was at the bottom of the scrum following a Chicago running play and stayed down for several minutes while medical personnel evaluated him.

Bears: G Kyle Long (ankle) and LB Lamarr Houston (knee) — both working their way back from surgery — topped the list of players held out by Chicago. RB Jeremy Langford (ankle) was not in uniform. … RB Ka’Deem Carey left with a quad injury.